As I mentioned, the same details are on every cheque you write out and you have no idea how many people then have access to that cheque.
In the case of Clarkson, a direct debit is not something an individual can setup to take money out of someone else's account (hence the reason who ever did signed him up for a charity) - the bank rulebook for a company to be able to set up direct debits is about an inch thick, it is far more hassle than it would be worth to try and steal money from an account.
John